Like many have suggested, there seems to be a few variables to your inconsistency. Without knowing more about what you've been doing to prepare, it is difficult for anyone to advise you on the topic. However, it is my experience that folks who are more prepared will see less outliers and more true data.
Can you let us know about what you've been doing to prepare? That would help us narrow our feedback and perhaps offer you more value on the subject.
i thought of GMAT in August but the actual preparation or struggle started in Dec. - post x'mass i could say.
i started with Kaplan
( the book i had even earlier than August ).
i finished on my level by Feb end. i took the two mock test of Kaplan
. i was not satisfied with 61% of hard copy test and 510 online.
i further bought MGMAT ( Quant + Verbal).
i finished almost 3/4 of MGMAT by April first week.
and retook Kaplan
test. the scores i gave above.
i think i was average with quant and weak with verbal. now after all this i dont know which area i am weak.
i never had timing problem with Quant but i have it now.
when i heard of the GMAT change (IR) , i planned to give it in May. i speed up with everything but now ?
and retook the test of Kaplan